1. Field of the Invention
The present invention relates to a medical radiographic apparatus capable of performing plane tomography or both plane tomography and curvature tomography, preferably used in dentistry or otorhinolaryngology, and the patient's head fixing device used in the medical radiographic apparatus.
2. Description of the Related Art
FIG. 15 is a side view showing the constitution of a conventional radiographic apparatus 100 commonly used for plane tomography and curvature tomography used in dentistry or otorhinolaryngology. This radiographic apparatus generally comprises a swivel arm 101, a lift main body 102, a patient frame 103, a post 104, and a base 105.
The swivel arm 101, which is formed roughly in a U-form, comprises an X-ray generator and a slit plate, which are attached to one end 101a thereof, a film cassette and a slit plate, which attached to the other end 101b thereof, and includes a built-in X-ray detecting means realized by a displacement drive mechanism of the film cassette or charge coupled device (CCD).
The area in the middle 101c of the swivel arm 101 is suspended from a holding frame 108 through swivel means 107, and this holding frame 108 is extended integrally from the ascending/descending main body 102. The swivel means 107 incorporates a swivel mechanism table for swiveling the swivel arm 101, and an XY table. Therefore, it is possible to swivel the swivel means 107 along the shape of the dental arch of the patient, so that a radiograph of the entire mouth can be taken, that is, panoramic radiography or curvature tomography may be realized.
Moreover, as explained specifically in the Japanese Patent Applications 4-139888 and 5-307170 previously filed by the present applicant, by moving the X-ray generator and X-ray detection plane in mutually parallel reverse directions while synchronized, and passing the irradiation X-rays constantly along the same region of the desired plane section by cooperating with the movement, a plane tomograph can be taken at an arbitrary section of the teeth, dentition, and mandibular joint.
The ascending/descending main body 102 is designed to move up and down in the vertical direction along a guide groove 106 on the post 104, by unlocking and manipulating an electromagnetic brake (not shown) or a lock handle 109, and when the electromagnetic brake is applied or when the lock handle 109 is locked, the ascending/descending main body 102 is fixed and supported on the post 104. The post 104 is planted on the base 105.
A handle 118 is provided at the lower side of the patient frame 103, and with the patient gripping this handle 118, the position of the patient 112 in radiography can be stabilized, while the shoulders of the patient 112 are lowered so as not to interfere with the movement of the swivel arm 101.
A header holder 114 for positioning and holding the head 113 of the patient 112 comprises a frontal holding member 115 abutting against the forehead of the head 113 of the patient 112, a pair of temporal holding members 116 abutting against the both temporal regions of the patient 112, and a chin rest 117a for resting the jaw of the patient 112. The head holding members 115, 116 are installed downward from the middle 101c of the swivel arm 101. The chin rest 117a is fixed to the patient frame 103 through a chin rest support member 117. Being fixed to the patient frame 103 or ascending/descending main body 102, it is free to move up and down together with the ascending/descending main body 102.
In a thus constituted radiographic apparatus 100, the radiologist adjusts the ascending/descending main body 102 by ascending or descending according to the height of the patient 112, displaces the chin rest 117a in the longitudinal direction of the patient 112, while expanding or contracting, and adjusts the exposure position of the head 113 to coincide with the X-ray irradiation plane, and then takes a radiograph.
In panoramic radiography, generally, an oblong film of 150.times.300 mm is used in almost the entire area, but in plane tomography, the irradiation field is about 70.times.80 mm, so that plural plane tomographs can be taken on one film for a panorama.
In dental treatment or orthodontic therapy, hitherto, so-called panoramic radiographing of the entire dental arch by using X-rays or tomography from an arbitrary direction near a target tooth has been utilized. In such a method, especially when observing the process, it is extremely important to assure its repeatability by always irradiating the site with the same dose of exposure. Furthermore, unless the head of the patient is fixed firmly, the formed image may deteriorate due to blurring or the like. Hence, the apparatus for fixing the head of the patient has been used.
FIG. 16 is a side view schematically showing a typical conventional head fixing device 301. This head fixing device 301 roughly comprises a pair of right and left temporal holding members 302, a chin rest 303, and guide means 304. First, while the pair of temporal holding members 302 are apart from each other, the patient places the head between the temporal holding members 302, and then the temporal holding members 302 come closer to each other, and protruding ear rods 305 provided at respective free ends 302a thereof are fitted into the external auditory meatus, so that the ears of the patient are positioned. Subsequently to this state, the main body 303b of the chin rest 303 is expanded or contracted in the direction of arrow 306 so that the lower jaw of the patient may be placed on a platform 303a of the chin rest 303, and is displaced in the direction of arrow 307 by guide means 304. In this way, the lower jaw of the patient is positioned, and while the oculoauricular horizontality is kept, that is, the line linking the external auditory meatus and the eye of the patient is horizontal, for example, the panoramic or tomographic picture is taken.
In the radiographic apparatus 100 applicable in both plane tomography and curvature tomography, however, it is difficult to take upper and lower remote positions correctly in the center of the irradiation field of the film, for example, when the mandibular joint is located in an upper position and the lower jaw end is located at a lower position.
Moreover, in the prior art in FIG. 16, in order to achieve the oculoauricular horizontality by varying the slant angle of the face of the patient, one must match the indication beam emitted from the ascending/descending main body or the like with the face of the patient, and then the expansion or contraction and displacement of the chin rest 303 must be repeated alternately, and thus controllability is poor. It is also the same in the construction for supporting the head of the patient from beneath the head as in the prior art shown in FIG. 16, or in the construction for fixing the head of the patient from above as being installed near the mounting part of the swivel arm.